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Any science teacher knows the power of a demonstration to bridge the gap between theory and physical experience. But not all science is easy to see, which is why researchers at Brigham Young University devised a novel way to show off a technique they study: time reversal.

Once called “matched signal processing,” the more evocatively-named time reversal is a technique to concentrate sound waves at a particular location. It’s used to direct vibrations in medical ultrasounds, and researchers think it could be the future of private communications.

Check out the video above to watch time reversal selectively knock over Lego figurines, and get a sense of how the decades-old but little-understood technique works.